I have reservations about installing as a service. My take on it is that Syncthing is an inherently user-level application. It synchronizes the user's files, with the user's permissions, using configuration from the user's AppData. It therefore needs to be run at the user, when the user logs in. Running it with elevated (LOCALADMIN) permissions is just asking for trouble in all sorts of places: file permissions, security - you've just opened an attack vector for people to edit previously-uneditable files, someone erroneously trying to sync Program Files or C:\Windows, etc. I'm not prepared to accept that level of responsibility. Configuration is another aspect: per-user configuration becomes nie-on impossible, unless I've missed a trick.
On the flip side, running a service as a particular user kind of defeats the point of services, and doesn't support multi-user computers (only the user the service is running as will be able to use Syncthing).
I think the 'Install Syncthing as a service with NSSM' craze started because a service is the most obvious way to start an application when the computer starts, assuming the original proponent forget about start-on-login.
If you can explain why those reservations are mis-founded, then I'm open to the possibility of installing a service. However this would take a while: I'd need to support tray utilities that both ran everything in one process (for the portable users - there are a few of them), and one that could get all the data it needs from IPC with a windows service. Not impossible by any means, but give me a couple of months